1. Field of the Invention
The present invention relates to centrifugal pumps and, more particularly, to a shrouded inducer for use with a centrifugal pump. The present invention is more particularly directed to eliminating the cavitation damage which normally would result from a recirculation flow of fluid about the shroud of the inducer.
2. Description of the Prior Art
The addition of a shroud to an otherwise shroudless inducer assists in preventing the formation of vortices at or about the tip of the inducer blades and thus minimizes the cavitation damage to the inducer associated with such vortices. The addition of a shroud, however, may cause a portion of the fluid downstream of the inducer to recirculate about the outer periphery of the shroud and then re-enter the main flow jets upstream of the inducer blade. As the recirculating fluid emerges from behind the forward or upstream edge of the shroud, it will often shed vortices which impinge directly upon the more radially outward portions of the inducer blades. These vortices create an erosive action upon portions of the blades and ultimately result in the inducer suffering a loss in efficiency and structural integrity. The use of a shroud to avoid the problems associated with blade tip vortices is exacerbated by the problems associated with vortices shed at the forward edge of the shroud.
Various attempts have been made to overcome the problems associated with recirculation flow about a shrouded inducer. For example, labyrinth seals have been placed about the outer periphery of the inducer shroud to minimize recirculation flow over the shroud. However, no matter how good the labyrinth seal, there is always some amount of flow which passes over the seal which will then cause the aforementioned vortices problem.
Moreover, as time goes by, labyrinth seals tend to lose their sealing effectiveness, especially in pumps where vibration and thermodynamics subject the seal to any degree of rubbing. An extensive use of labyrinth seals could be employed to reduce the circulation flow to a minimum such as suggested in U.S. Pat. No. 2,984,189. Such an extensive use of seals is impractical and costly. Various other methods have been proposed with regard to the construction of a shrouded inducer to overcome the problems associated with vortices emanating from the shroud.